here is my overarching theory in a nutshell... in the world of LOST, time as we all would experience it does not "naturally" flow in a linear manner. it is scattershot like in slaughterhouse five. however at some point four-toed aliens came along and built a machine that made time flow in a linear manner, a way that humans can comprehend. that machine is the island. the island is very important. it is a lock on time, making it run straight. but all locks can be picked. so there must be a lock on the lock. and locke is the lock on the lock. he is what will or will not keep the island (a machine that keeps time flowing in a logical way in which humans can experience life without going nuts) working properly.
robartes